Electronic Insertion

Using electronic wizardry, you can punch a ‘hole’ or matte in a master shot, and insert there the exactly corresponding area of a background picture.

Keyed insertion

The SEG (special effects generator) is usually part of the switcher facilities. It automatically interswitches between pictures to produce:

• Uncover wipe patterns – removing a section reveals another shot.

• Split-screens • subdividing the frame, to show parts of two shots.

• Insets/inserts – displaying a section from another shot, within the main picture.

You can select various adjustable geometrical shapes, with hard or soft (diffused) edges, and position them anywhere in the screen. A variation on this method uses a silhouette graphic placed in front of a supplementary camera, to provide the matting. You can make this camera matte any shape, and expand/contract it by zooming.

Chromakey (CSC)

Wherever blue appears in the subject/master shot, this system automatically switches to the background scene from another video source instead. So a person in front of a blue surface appears ‘inserted’ into the other shot. The background scene itself can contain any colors.

You can create elaborate ‘multi-layer’ effects or ‘multiple images’, by using this composite picture as the ‘background’ for other insertions.

Take care

If you are not careful; though, strange effects can develop:

• Limitations. Anything moving outside an ‘inserted’ area will be cut off or vanish. Chromakey subjects normally move in front of the background shot.

• Background breakthrough. Occurs if the hue you are using for switching (usually blue) is worn or reflected by the subject

• Incongruities. Incorrect scale, wrong proportions or perspective, ridiculous situations (e.g. standing in space).

• Accidental effects. Both foreground and background cameras’ shots must be held still. Panning/tilting causes ‘flying’. Zooming causes growing/shrinking.

• Some chromakey systems will insert cast shadows of the subject. In others, shadows cause spurious breakthrough.

Typical applications

• To insert a closeup shot within the main picture.

• To imitate a wall display screen, or a window in a setting.

• To place a person ‘within’ a photographic background or model.

• To use photographs, artwork, models (miniatures) as the background for action, instead of built settings.

• To create scale changes such as giant animals, tiny people, growing/shrinking.

• To produce magical effects such as appearances/disappearances (total or partial), people flying or falling from a height.

• To form ‘living paintings’ in which you brush the canvas with the keying hue, and the subject appears.

• External keying circuits insert ‘solid’ titling into pictures.

Using chromakey

The master Camera 1 sees the subject in front of a blue background. Wherever the keying amplifier ‘sees’ blue in the shot, it switches to the background picture on Camera 2. When combined, the subject appears ‘in’ the background shot.

Insets

Part of one shot can beinserted into another, by using a simple corner wipe – hard or soft-edged.